Graphene oxide–ZnO nanocomposite: an efficient visible light photocatalyst for degradation of rhodamine B

ZnO/Graphene Oxide on Halloysite Nanotubes as a Superabsorbent Nanocomposite Photocatalyst for the Degradation of Organic Dyes

Using renewable photocatalysts for pollutant degradation represents a promising approach to addressing environmental water challenges by harnessing solar energy without additional energy consumption. However, for the practical use of photocatalysts, it is necessary to improve catalyst efficiency, considering cost and biocompatibility. In this study, we developed a new superabsorbent photocatalyst for the degradation of organic dyes in water. Our photocatalyst comprises halloysite nanotubes (HNTs) with a large outer diameter and Si-O and Al-O groups on the outer and inner surfaces, respectively; graphene oxide (GO) possessing numerous sp2 bonds and light-conductive properties; and ZnO, which can degrade organic molecules via a photon source. By exploiting the superabsorbent properties of GOs for organic dyes and stabilizing ZnO nanoparticles on HNTs to inhibit aggregation, our photocatalysts demonstrated significantly improved degradability compared to ZnO nanoparticles alone and combinations of ZnO with HNTs or GO. The structural characteristics of the nanocomposites were characterized using SEM, EDX, Raman spectroscopy, and XRD. Their enhanced photocatalytic activity was demonstrated by the degradation of rhodamine b in water, showing 95% photodegradation under UV illumination for 60 min, while the ZnO nanoparticles showed only 56% dye degradation under the same condition. Additionally, the degradation rate was enhanced by four times. Furthermore, the catalysts maintained their initial activity with no significant loss after four uses, showing their potential for practical implementation in the mass purification of wastewater.

Catalytic-CO2-Desorption Studies of BZA-AEP Mixed Absorbent by the Lewis Acid Catalyst CeO2-γ-Al2O3

Traditional organic amines exhibit inferior desorption performance and high regeneration energy consumption. The implementation of solid acid catalysts presents an efficacious approach to mitigate regeneration energy consumption. Thus, investigating high-performance solid acid catalysts holds paramount importance for the advancement and implementation of carbon capture technology. This study synthesized two Lewis acid catalysts via an ultrasonic-assisted precipitation method. A comparative analysis of the catalytic desorption properties was conducted, encompassing these two Lewis acid catalysts and three precursor catalysts. The results demonstrated that the CeO₂-γ-Al₂O₃ catalyst demonstrated superior catalytic desorption performance. Within the desorption temperature range of 90 to 110 °C, the average desorption rate of BZA-AEP catalyzed by the CeO₂-γ-Al₂O₃ catalyst was 87 to 354% greater compared to the desorption rate in the absence of the catalyst, and the desorption temperature can be reduced by approximately 10 °C. A comprehensive analysis of the catalytic desorption mechanism of the CeO₂-γ-Al₂O₃ catalyst was conducted, and indicated that the synergistic effect of CeO₂-γ-Al₂O₃ conferred a potent catalytic influence throughout the entire desorption process, spanning from the rich solution to the lean solution.

Control of Explosive Chemical Reactions by Optical Excitations: Defect-Induced Decomposition of Trinitrotoluene at Metal Oxide Surfaces

Interfaces formed by high energy density materials and metal oxides present intriguing new opportunities for a large set of novel applications that depend on the control of the energy release and initiation of explosive chemical reactions. We studied the role of structural defects at a MgO surface in the modification of electronic and optical properties of the energetic material TNT (2-methyl-1,3,5-trinitrobenzene, also known as trinitrotoluene, C₇H₅N₃O₆) deposited at the surface. Using density functional theory (DFT)-based solid-state periodic calculations with hybrid density functionals, we show how the control of chemical explosive reactions can be achieved by tuning the electronic structure of energetic compound at an interface with oxides. The presence of defects at the oxide surface, such as steps, kinks, corners, and oxygen vacancies, significantly affects interfacial properties and modifies electronic spectra and charge transfer dynamics between the oxide surface and adsorbed energetic material. As a result, the electronic and optical properties of trinitrotoluene, mixed with an inorganic material (thus forming a composite), can be manipulated with high precision by interactions between TNT and the inorganic material at composite interfaces, namely, by charge transfer and band alignment. Also, the electron charge transfer between TNT and MgO surface reduces the decomposition barriers of the energetic material. In particular, it is shown that surface structural defects are critically important in the photodecomposition processes. These results open new possibilities for the rather precise control over the decomposition initiation mechanisms in energetic materials by optical excitations.

Marine Collagen-Based Antibacterial Film Reinforced with Graphene and Iron Oxide Nanoparticles

It has become more widely available to use biopolymer-based films as alternatives to conventional plastic-based films due to their non-toxic properties, flexibility, and affordability. However, they are limited in application due to deficiencies in their properties. The marine collagen was the specimen for the present study. Thus, the main objective was to reinforce marine collagen-based films with 1.0% (w/w of the dry polymer weight) of iron oxide nanoparticles (IO-NPs), graphene oxide nanoparticles (GO-NPs), or a combination of both oxides (GO-NPs/IO-NPs) as antibacterial and antioxidant additives to overcome some of the limitations of the film. In this way, the nanoparticles were incorporated into the film-forming solution (2% w/v in acetic acid, 0.05 M) and processed by casting. Thereafter, the films were dried and analyzed for their physicochemical, mechanical, microstructural, and functional properties. The results show that the effective combination of GO-NPs/IO-NPs enhanced the physicochemical properties by increasing the water contact angle (WCA) of the films from 77.2 to 84.4° and their transparency (T) from 0.5 to 5.2. Furthermore, these nanoparticles added antioxidant and antibacterial value to the films, with free radical inhibition of up to 95.8% and 23.8 mm of bacteria growth inhibition (diameter). As a result, both types of nanoparticles are proposed as suitable additives to be incorporated into films and enhance their different properties.

Heterostructured Photocatalysts Associating ZnO Nanorods and Ag-In-Zn-S Quantum Dots for the Visible Light-Driven Photocatalytic Degradation of the Acid Orange 7 Dye

Heterostructured photocatalysts associating ZnO nanorods (NRs) sensitized by quaternary Ag-In-Zn-S (AIZS) quantum dots (QDs) were prepared by depositing AIZS QDs at the surface of ZnO NRs followed by thermal treatment at 300 °C. The ZnO/AIZS catalysts were characterized by X-ray diffraction, electron microscopy, UV-vis diffuse spectroscopy and by photoelectrochemical measurements. Their photocatalytic activity was evaluated for the bleaching of the Acid Orange 7 (AO7) dye under visible light irradiation. Results show that the association of ZnO NRs with 10 wt% AIZS QDs affords the photocatalyst the highest activity due to the enhanced visible light absorption combined with the improved charge separation. The ZnO/AIZS(10) photocatalyst degrades 98% AO7 in 90 min under visible light illumination, while ZnO NRs can only decompose 11% of the dye. The ZnO/AIZS(10) photocatalyst was also found to be stable and can be reused up to eight times without significant alteration of its activity. This work demonstrates the high potential of AIZS QDs for the development of visible light active photocatalysts.

Synthesis, Characterization, and Performance Evaluation of Hybrid Waste Sludge Biochar for COD and Color Removal from Agro-Industrial Effluent

Agro-waste management processes are evolving through the development of novel experimental approaches to understand the mechanisms in reducing their pollution levels efficiently and economically from industrial effluents. Agro-industrial effluent (AIE) from biorefineries that contain high concentrations of COD and color are discharged into the ecosystem. Thus, the AIE from these biorefineries requires treatment prior to discharge. Therefore, the effectiveness of a continuous flow bioreactor system (CFBS) in the treatment of AIE using hybrid waste sludge biochar (HWSB) was investigated. The use of a bioreactor with hydraulic retention time (HRT) of 1–3 days and AIE concentrations of 10–50% was used in experiments based on a statistical design. AIE concentration and HRT were optimized using response surface methodology (RSM) as the process variables. The performance of CFBS was analyzed in terms of COD and color removal. Findings indicated 76.52% and 66.97% reduction in COD and color, respectively. During biokinetic studies, the modified Stover models were found to be perfectly suited for the observed measurements with R2 values 0.9741 attained for COD. Maximum contaminants elimination was attained at 30% AIE and 2-day HRT. Thus, this study proves that the HWSB made from biomass waste can potentially help preserve nonrenewable resources and promote zero-waste attainment and principles of circular economy.

Palladium and Graphene Oxide Doped ZnO for Aqueous Acetamiprid Degradation under Visible Light

Acetamiprid is a neonicotinoid insecticide widely used in pest control. In recent years, it has been considered as a contaminant in groundwater, lakes, and rivers. Photocatalysis under visible light radiation proved to be an effective process for getting rid of several organic pollutants. In the present work, photodegradation of aqueous acetamiprid was investigated over bare zinc oxide (ZnO) photocatalyst as well as ZnO doped with either palladium or palladium combined with graphene oxide. Both ZnO and doped-ZnO were synthesized via a microwave-assisted hydrothermal procedure. The obtained photocatalysts were characterized using different techniques. After 5 h of reaction at ambient temperature under visible light irradiation, acetamiprid conversions attained ca. 38, 82, and 98% in the presence of bare ZnO, Pd-doped ZnO and Pd-GO-doped ZnO photocatalysts, respectively, thus demonstrating the positive effect of Pd- and GO-doping on the photocatalytic activity of ZnO. In addition, Pd-GO-doped ZnO was shown to keep its activity even when it is recycled five times, thus proving its stability in the reaction medium.

Modifications of Polymers through the Addition of Ultraviolet Absorbers to Reduce the Aging Effect of Accelerated and Natural Irradiation

The photooxidative degradation process of plastics caused by ultraviolet irradiation leads to bond breaking, crosslinking, the elimination of volatiles, formation of free radicals, and decreases in weight and molecular weight. Photodegradation deteriorates both the mechanical and physical properties of plastics and affects their predicted life use, in particular for applications in harsh environments. Plastics have many benefits, while on the other hand, they have numerous disadvantages, such as photodegradation and photooxidation in harsh environments and the release of toxic substances due to the leaching of some components, which have a negative effect on living organisms. Therefore, attention is paid to the design and use of safe, plastic, ultraviolet stabilizers that do not pose a danger to the environment if released. Plastic ultraviolet photostabilizers act as efficient light screeners (absorbers or pigments), excited-state deactivators (quenchers), hydroperoxide decomposers, and radical scavengers. Ultraviolet absorbers are cheap to produce, can be used in low concentrations, mix well with polymers to produce a homogenous matrix, and do not alter the color of polymers. Recently, polyphosphates, Schiff bases, and organometallic complexes were synthesized and used as potential ultraviolet absorbers for polymeric materials. They reduced the damage caused by accelerated and natural ultraviolet aging, which was confirmed by inspecting the surface morphology of irradiated polymeric films. For example, atomic force microscopy revealed that the roughness factor of polymers' irradiated surfaces was improved significantly in the presence of ultraviolet absorbers. In addition, the investigation of the surface of irradiated polymers using scanning electron microscopy showed a high degree of homogeneity and the appearance of pores that were different in size and shape. The current work surveys for the first time the use of newly synthesized, ultraviolet absorbers as additives to enhance the photostability of polymeric materials and, in particular, polyvinyl chloride and polystyrene, based mainly on our own recent work in the field.

Structural and Electrical Characterization of Pure and Al-Doped ZnO Nanorods

Pure and Al-doped (3 at.%) ZnO nanorods were prepared by two-step synthesis. In the first step, ZnO thin films were deposited on silicon wafers by spin coating; then, ZnO nanorods (NR) and Al-doped ZnO NR were grown using a chemical bath method. The structural properties of zincite nanorods were determined by X-ray diffraction (XRD) and corroborated well with the morphologic properties obtained by field-emission gun scanning electron microscopy (FEG SEM) with energy-dispersive X-ray spectroscopy (EDS). Morphology results revealed a minute change in the nanorod geometry upon doping, which was also visible by Kelvin probe force microscopy (KPFM). KPFM also showed preliminary electrical properties. Detailed electrical characterization of pure and Al-doped ZnO NR was conducted by temperature-dependent current–voltage (I–V) measurements on Au/(Al)ZnO NR/n-Si junctions. It was shown that Al doping increases the conductivity of ZnO NR by an order of magnitude. The I–V characteristics of pure and Al-doped ZnO NR followed the ohmic regime for lower voltages, whereas, for the higher voltages, significant changes in electric conduction mechanisms were detected and ascribed to Al-doping. In conclusion, for future applications, one should consider the possible influence of the geometry change of (Al)ZnO NRs on their overall electric transport properties.

Floating Carbon-Doped TiO2 Photocatalyst with Metallic Underlayers Investigation for Polluted Water Treatment under Visible-Light Irradiation

In the current study, we analysed the influence of metallic underlayers on carbon-doped TiO2 films for RhB decomposition and Salmonella typhimurium inactivation under visible-light irradiation. All the experiments were divided into two parts. First, layered M/C-doped-TiO2 film structures (M = Ni, Nb, Cu) were prepared by magnetron sputtering technique on borosilicate glass substrates in the two-step deposition process. The influence of metal underlayer on the formation of the carbon-doped TiO2 films was characterised by X-ray diffractometer, scanning electron microscope, and atomic force microscope. The comparison between the visible-light assisted photocatalytic activity of M/C-doped TiO2 structures was performed by the photocatalytic bleaching tests of Rhodamine B dye aqueous solution. The best photocatalytic performance was observed for Ni/C-doped-TiO2 film combination. During the second part of the study, the Ni/C-doped-TiO2 film combination was deposited on high-density polyethylene beads which were selected as a floating substrate. The morphology and surface chemical analyses of the floating photocatalyst were performed. The viability and membrane permeability of Salmonella typhimurium were tested in cycling experiments under UV-B and visible-light irradiation. Three consecutive photocatalytic treatments of fresh bacteria suspensions with the same set of floating photocatalyst showed promising results, as after the third 1 h-long treatment bacteria viability was still reduced by 90% and 50% for UV-B and visible-light irradiation, respectively. The membrane permeability and ethidium fluorescence results suggest that Ni underlayer might have direct and indirect effect on the bacteria inactivation process. Additionally, relatively low loss of the photocatalyst efficiency suggests that floating C-doped TiO2 photocatalyst with the Ni underlayer might be seen as the possible solution for the used photocatalyst recovery issue.

Facile synthesis of nitrogen-defective g-C3N4 for superior photocatalytic degradation of rhodamine B

Developing a new photocatalyst for fast and highly efficient organic dye degradation plays an essential role in wastewater treatment. In this study, a photocatalyst graphite phase carbon nitride (g-C₃N₄) containing nitrogen defects (CN) is reported for the degradation of rhodamine B (RhB). The porous g-C₃N₄ photocatalyst is facilely synthesized through a polycondensation method and then characterized by X-ray diffraction (XRD), infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FESEM), N₂ isotherm adsorption line, and X-ray photoelectron spectroscopy (XPS). The photocatalytic activity of the g-C₃N₄ is evaluated through the degradation of RhB under visible light irradiation. The results show that photocatalytic activity of the nitrogen-defective g-C₃N₄ can be improved by optimizating washing conditions, including washing temperature, washing dosage, drying time, and drying temperature. With the prepared nitrogen-defective g-C₃N₄, decolourization of RhB is able to be completed within 20 minutes, in which the degradation rate is 1.7 times higher than that of bulk g-C₃N₄. Moreover, the nitrogen-defective g-C₃N₄ has high stability and reusability in the degradation of RhB. Photocatalytic degradation mechanism investigations by ultraviolet-visible absorption spectroscopy, radical trapping experiments and high-performance liquid chromatography (HPLC) reveal that RhB achieved complete mineralization through the photocatalytic degradation reaction mediated by superoxide radicals (˙O₂⁻). This work thus provides a new approach for the preparation of photocatalysts for organic pollutants treatment in wastewater samples.

Nitrogen-defective g-C₃N₄ is synthesized and characterized as the photocatalyst for degradation of organic dyes, such as rhodamine B, in wastewater.

Utilization of Mangifera indica as Substrate to Bioremediate the Toxic Metals and Generate the Bioenergy through a Single-Chamber Microbial Fuel Cell

Microbial fuel cells (MFCs) are a sustainable approach for the remediation of metals and the simultaneous production of energy. This paper highlighted the usage of mango extract to produce electricity as an organic source for bacteria and reduce metal ions from wastewater. The observed results were 51 mV in 15 days with 500 Ω of external resistance. The whole operation was carried out at room temperature. The observed current and power density were 28.947 mA/m2 and 0.972 mW/m2, respectively. The internal resistance was 150 Ω, which is lower than external resistance. The remediation performance varied with the metal ions as follows: Pb (II) shows 75%, Cd (II) shows 74.11%, and Cr (III) shows 80.50%. Finally, the detailed working mechanism of the present study, MFC challenges, and future research directions are covered in this paper.

Microbial Fuel Cell: Recent Developments in Organic Substrate Use and Bacterial Electrode Interaction

A new bioelectrochemical approach based on metabolic activities inoculated bacteria, and the microbial fuel cell (MFC) acts as biocatalysts for the natural conversion to energy of organic substrates. Among several factors, the organic substrate is the most critical challenge in MFC, which requires long-term stability. The utilization of unstable organic substrate directly affects the MFC performance, such as low energy generation. Similarly, the interaction and effect of the electrode with organic substrate are well discussed. The electrode-bacterial interaction is also another aspect after organic substrate in order to ensure the MFC performance. The conclusion is based on this literature view; the electrode content is also a significant challenge for MFCs with organic substrates in realistic applications. The current review discusses several commercial aspects of MFCs and their potential prospects. A durable organic substrate with an efficient electron transfer medium (anode electrode) is the modern necessity for this approach.